As a rookie with the Bears in 1975, Avellini started four games on a team that finished 4-10. He threw for 942 yards with 6 TD passes along with 11 interceptions. Fully established as the Bears starter in 1976, he started all fourteen games, throwing for 1580 yards, although with a bad "td pass/int" ratio of 8/15. Chicago did improve to a 7-7 mark. Avellini improved on those numbers in 1977, passing for 2004 yards while once again starting every game for the Bears. However, once again his interception rate was rather high, throwing 18 picks compared to only 11 touchdown passes. The Bears again showed improvement as they ended up tying the Minnesota Vikings for the NFC Central title at 9-5 and earning a trip to the playoffs as the wildcard team – where they were handily beaten by the Dallas Cowboys. Walter Payton’s big season, where he piled up over 1,800 yards rushing, had a lot to do with their success. In 1978, the Bears would struggle, as they started 4-8 with Avellini under center, as he continued to pile up interceptions with 16 – while only tossing 5 TD passes. This caused coach Neill Armstrong to make a switch at quarterback – as he inserted veteran Mike Phipps into the starting role. Phipps – who the Bears had traded their first-round pick in the 1978 draft to acquire from Cleveland – promptly won three out of the final four games, to establish himself as the starter for the next season. The Bears would surprisingly roll to a 10-6 record in 1979 – which would tie Tampa Bay for the division title – and Avellini would now be in a backup role. He would continue in this capacity – playing behind Phipps, Vince Evans and Jim McMahon – until the 1984 season, seeing little action on the field. In 1984 – with the Bears starting 2-0 – Jim McMahon was injured and Mike Ditka inserted Bob Avellini in as the starter for a road game against Green Bay. Avellini had only started five games since the end of the 1978 season. The Bears could muster little offense with Avellini at the controls, but still managed to edge out the Packers 9-7. Chicago continued to struggle the next week as they were soundly beaten by Seattle 38-9. This resulted in Avellini being cut from the Bear’s roster by Ditka – and thus ending his decade-long tenure with Chicago. Avellini later signed on with the New York Jets where he would end his playing career after the 1984 season. The Bears, meanwhile, would go to the NFC Championship game that season and then win the Super Bowl the next season. made a brief comeback in 1986 with the Dallas Cowboys starting 3 preseason games but was released as the final cut.He then spent two years with The Ottawa Roughriders of The CFL wher he won 1987 Grey Cup and winning the games MVP award.He came back to NFL in 1989 to play with The Oakland Raiders seeing action in 7 games.he retired after the 1989 season